Efficient photon-to-electron conversion is a desirable material property for photovoltaic applications. The photon-to-electron conversion efficiency needs to be unity (purely radiative recombination) for solar cells to achieve the Shockley-Qucisser limit. CdTe possesses the preferable optical properties for photovoltaic (PV) applications: a near optimum bandgap of 1.5 eV, and a high absorption coefficient of over 15,000 cm−1 at the band edge.
CdTe thin-film solar cell technology is considered to be quite promising because polycrystalline CdTe possesses a close-to-optimum bandgap of 1.45 eV and a high absorption coefficient of over 15,000 cm−1 at the band edge. The detailed-balance limit efficiency is about 32% with an open-circuit voltage (Voc) of 1.17 V in the presence of the AM1.5G radiation. Power-conversion efficiency for a CdTe solar cell of about 22% (and module efficiency of about 19%) were demonstrated in the laboratory, which at least equals to or even surpasses multi-crystalline silicon module efficiency (18.5%). And yet, these efficiency values are still below both the Shockley-Queisser limit and the record efficiencies demonstrated by single-crystalline Si (25.6%) and GaAs (28.8%) solar cells. The current manufacturing process includes multiple steps, some of which, such as p-type back contact, for example, presents major practical challenges. Notably, the record energy conversion efficiency for a single-crystalline CdTe solar has not changed since the 1980s. Therefore, there remains a need for improvement of efficiency of CdTe-based heterostructures and CdTe thin-film solar-cell manufacturing based on such heterostructures. The question of whether it is possible to achieve much higher valued of VOC than in the polycrystalline materials also requires an answer.